Optical systems and methods and optical amplifiers for use therein

ABSTRACT

Optical transmission systems of the present invention include at least one optical amplifier in which pump power being provided to an amplifying medium is amplified using a pump amplifier prior to being introduced into the amplifying medium. In various embodiments, a cascaded Raman resonator is used as a pump booster source to provide Raman amplification of the pump power being supplied from one or more pump sources to the signal channel amplifying medium.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.09/998,525, now U.S. Pat. No. 6,459,529 filed Nov. 30, 2001, which is acontinuation of U.S. patent application Ser. No. 09/517,661, now U.S.Pat. No. 6,344,925 filed Mar. 3, 2000, both of which are incorporatedherein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

BACKGROUND OF THE INVENTION

The present invention is directed generally to optical transmissionsystems. More particularly, the invention is directed toward opticaltransmission systems including higher performance optical amplifiers.

Digital technology has provided electronic access to vast amounts ofinformation. The increased access has driven demand for faster andhigher capacity electronic information processing equipment (computers)and transmission networks and systems to link the processing equipment.

In response to this demand, communications service providers have turnedto optical communication systems, which have the capability to providesubstantially larger information transmission capacities thantraditional electrical communication systems. Information can betransported through optical systems in audio, video, data, or othersignal format analogous to electrical systems. Likewise, optical systemscan be used in telephone, cable television, LAN, WAN, and MAN systems,as well as other communication systems.

Early optical transmission systems, known as space division multiplex(SDM) systems, transmitted one information signal using a singlewavelength in separate waveguides, i.e. fiber optic strand. Thetransmission capacity of optical systems was increased by time divisionmultiplexing (TDM) multiple low bit rate, information signals into ahigher bit rate signals that can be transported on a single opticalwavelength. The low bit rate information carried by the TDM opticalsignal can then be separated from the higher bit rate signal followingtransmission through the optical system.

The continued growth in traditional communications systems and theemergence of the Internet as a means for accessing data has furtheraccelerated the demand for higher capacity communications networks.Telecommunications service providers, in particular, have looked towavelength division multiplexing (WDM) to further increase the capacityof their existing systems.

In WDM transmission systems, pluralities of distinct TDM or SDMinformation signals are carried using electromagnetic waves havingdifferent wavelengths in the optical spectrum, typically in the infraredportion of the spectrum. The pluralities of information carryingwavelengths are combined into a multiple wavelength WDM optical signalthat is transmitted in a single waveguide. In this manner, WDM systemscan increase the transmission capacity of existing SDM/TDM systems by afactor equal to the number of wavelengths used in the WDM system.

Optical WDM systems were not initially deployed, in part, because of thehigh cost of electrical signal regeneration equipment requiredapproximately every 20-50 km to compensate for signal attenuation foreach optical wavelength throughout the system. The development of theerbium doped fiber optical amplifier (EDFA) provided a cost effectivemeans to optically amplify attenuated optical signal wavelengths in the1550 nm range. In addition, the 1550 nm signal wavelength rangecoincides with a low loss transmission window in silica based opticalfibers, which allowed EDFAs to be spaced further apart than conventionalelectrical regenerators.

The use of EDFAs essentially eliminated the need for, and the associatedcosts of, electrical signal regeneration/amplification equipment tocompensate for signal attenuation in many systems. The dramaticreduction in the number of electrical regenerators in the systems, madethe installation of WDM systems in the remaining electrical regeneratorsa cost effective means to increase optical network capacity.

WDM systems have quickly expanded to fill the limited amplifierbandwidth of EDFAs. New erbium-based fiber amplifiers (L-band) have beendeveloped to expand the bandwidth of erbium-based optical amplifiers.Also, new transmission fiber designs are being developed to provide forlower loss transmission in the 1380-1530 nm and 1600-1700 nm ranges toprovide additional capacity for future systems.

Raman fiber amplifiers (“RFAs”) are also being investigated for use inwide bandwidth, e.g., 100 nm, optical amplifiers, but RFAs generallymake less efficient use of pump power than EDFAs. Therefore, RFAs havenot been deployed in commercial systems because significant pump powerson the order of hundreds of milliwatts are required to achieve therequired levels of amplification.

RFAs do, however, have appeal as a viable option for next generationoptical amplifiers, because RFAs provide low noise, wide bandwidths, andwavelength flexible gain.

Commonly assigned U.S. patent application Ser. Nos. 09/119,556 and09/253,819, which are incorporated herein by reference, describe RFAsthat can be deployed in existing fiber optic networks having variousfiber designs and compositions and over a wide range of signalwavelengths.

RFAs are theoretically scalable to provide amplification over a range ofbandwidths and power. However, the amplification bandwidth and power islimited, in part, by the amount of pump power that can be delivered tothe fiber amplifier. The capability to provide higher pump powers isessential for continued development of optical amplifiers and opticalsystems to meet the requirements of next generation optical systems.

BRIEF SUMMARY OF THE INVENTION

The systems, apparatuses, and methods of the present invention addressthe above needs to provide higher performance optical amplifiers andsystems. The optical systems generally include at least one opticaltransmitter configured to transmit information via at least one opticalsignal wavelength, or channel, to at least one optical receiver viaoptical transmission media, such as an optical fiber. The system willalso include at least one optical amplifier disposed between thetransmitters and receivers to overcome various signal power losses, suchas media attenuation, combining, splitting, etc. in the system.

The optical amplifier will generally include an optical signalamplifying medium supplied with pump power in the form of optical energyin one or more pump wavelengths via an optical pump source. The pumpsource can include one or more optical sources, such as narrow and broadband lasers or other coherent, as well as incoherent sources.

The optical amplifier will further include a pump amplifier configuredto amplify the pump power being supplied to the signal amplifying media.In various embodiments, the pump amplifier includes a pump amplifyingmedium supplied with pump booster power in the form of optical energyfrom a pump booster source. The pump amplifying medium can includevarious amplifying fibers as may be appropriate for amplifying the pumppower. The pump amplifier can be configured to provide Ramanamplification of the pump power being supplied to at least oneamplifying media to optically amplify signal wavelengths passing throughthe amplifying media. For example, the pump booster power can besupplied in the 1300-1450 range to provide Raman amplification of pumpwavelengths in the 1400-1500 range in the pump amplifier.

In addition, the pump booster power can be split and used to amplifypump power being supplied to multiple optical amplifiers disposed alongone or more transmission fibers. In this manner, the pump booster power,which can be several watts, and the cost of the pump booster source canbe spread over a number of amplifiers in the system. It may be also bedesirable to combine the power from two or more pump booster sourceprior to splitting the pump booster power to amplify the RFA pumpwavelengths to provide additional redundancy in the system.

In various embodiments, a cascaded Raman resonator (“CRR”) and/orsemiconductor laser diodes can be used as the pump booster source toprovide pump booster power to amplify the pump power provided by thepump sources. The pump power supplied by each of the optical sources inthe pump source can be varied to control the overall pump powerdistribution over the pump wavelength range.

In various CRR embodiments, CRR input power in at least one inputwavelength is introduced into a fiber Raman resonator ring via an inputwavelength division multiplexing (WDM) coupler. An output WDM coupler isfurther coupled to resonator ring to output the pump booster power at anappropriate wavelength to supply optical energy for use in the pumpamplifying fiber.

The use of pump amplifier external to the transmission fiber in thepresent invention provides flexibility in the optical amplifier design.For example, lower power optical sources can be employed in the pumpsources, thereby reducing component costs in the system. The opticalsources can be individually controlled and fine tuned before the pumppower is amplified. When Raman pump amplifiers are used, the wavelengthand relative power of the optical sources can be varied within the Ramangain bandwidth of the pump amplifier to vary the wavelength profile ofthe pump power provided to the amplifier without changing the pumpamplifier. Thus, the optical amplifiers of the present invention provideincreased power, control, flexibility, and upgradability necessary forhigher performance optical systems. These advantages and others willbecome apparent from the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described, by way ofexample only, with reference to the accompanying drawings for thepurpose of illustrating present embodiments only and not for purposes oflimiting the same, wherein like members bear like reference numeralsand:

FIGS. 1 and 2 show optical system embodiments;

FIGS. 3-4 show optical amplifier embodiments; and,

FIGS. 5-7 show various optical amplifier and pump amplifier embodiments.

DETAILED DESCRIPTION OF THE INVENTION

Optical systems 10 of the present invention include an optical amplifier12 disposed along an optical transmission medium, such as an opticalfiber 14, to optically amplify optical signals passing between opticalprocessing nodes 16. One or more transmitters 18 can be included in thenodes 16 and configured to transmit information via the optical signalsin one or more information carrying signal wavelengths, or signalchannels, λ_(si) to one or more optical receivers 20 in other nodes 16.The optical system 10 can be controlled by a network management system22 and configured in multi-dimensional networks (FIG. 1) or in one ormore serially connected point to point links (FIG. 2). The networkmanagement system 22 can communicate with the various nodes and elementsin the optical systems 10 via wide area networks external to the system10 and/or supervisory optical channels within the system 10.

The optical processing nodes 16 may also include other opticalcomponents, such as one or more add/drop devices and optical andelectrical switches/routers/cross-connects 21 interconnecting thetransmitters 18 and receivers 20. For example, broadcast and/orwavelength reusable, add/drop devices, and optical andelectrical/digital cross connect switches and routers can be configuredvia the network management system 22 in various topologies, i.e., rings,mesh, etc. to provide a desired network connectivity.

The transmitters 18 used in the system 10 will generally include anarrow bandwidth laser optical source that provides an optical carrier.The transmitters 18 also can include other coherent narrow or broad bandsources, such as sliced spectrum sources, as well as suitable incoherentoptical sources as appropriate. Information can be imparted to theoptical carrier either by directly modulating the optical source or byexternally modulating the optical carrier emitted by the source.Alternatively, the information can be imparted to an electrical carrierthat can be upconverted using the optical carrier onto an opticalwavelength to produce the optical signal. Similarly, the opticalreceiver 20 used in the present invention can include various detectiontechniques, such coherent detection, optical filtering and directdetection, and combinations thereof. Employing tunable transmitters 18and receivers 20 in the optical nodes 16 in a network, such as in FIG.2, can provide additional versatility in the system 10.

The transmitters 18 and receivers 20 can be also connected tointerfacial devices 23, such as electrical and optical cross-connectswitches, IP routers, etc., to provide interface flexibility within, andat the periphery of, the optical system 10. The interfacial devices 23can be configured to receive, convert, and provide information in one ormore various protocols, encoding schemes, and bit rates to thetransmitters 22, and perform the converse function for the receivers 24.The interfacial devices 23 also can be used to provide protectionswitching in various nodes 16 depending upon the configuration.

Generally speaking, N transmitters 18 can be used to transmit Mdifferent signal wavelengths to J different receivers 20. In variousembodiments, one or more of the transmitters 18 and/or receivers 20 canbe wavelength tunable to provide wavelength allocation flexibility inthe optical system 10. In addition, the system 10 can also be configuredto carry uni- and bi-directional traffic.

Optical combiners 24 can be used to combine the multiple signal channelsinto WDM optical signals and pump wavelengths λ_(pi). Likewise, opticaldistributors 26 can be provided to distribute the optical signal to thereceivers 20 _(j) and optical signal and pump wavelengths λ_(pi) tomultiple paths. The optical combiners 24 and distributors 26 can includevarious multi-port devices, such as wavelength selective andnon-selective (“passive”), fiber and free space devices, as well aspolarization sensitive devices. The multi-port devices can variousdevices, such as circulators, passive, WDM, and polarizationcouplers/splitters, dichroic devices, prisms, diffraction gratings,arrayed waveguides, etc. The multi-port devices can be used alone or invarious combinations along with various tunable or fixed wavelengthfilters in the optical combiners 24 and distributors 26. The filters caninclude various transmissive or reflective, narrow or broad bandfilters, such as Bragg gratings, Mach-Zehnder, Fabry-Perot and dichroicfilters, etc. Furthermore, the combiners 24 and distributors 26 caninclude one or more stages incorporating various multi-port device andfilter combinations to multiplex, consolidate, demultiplex, multicast,and/or broadcast signal channels λ_(si) and pump wavelengths λ_(pi) inthe optical systems 10.

The optical amplifiers 12 generally include an optical amplifying medium30 supplied with power from an amplifier power source 32 as shown inFIG. 3. For the sake of clarity, the optical amplifier 12 will begenerally described in terms of an amplifying fiber 34 supplied withpump power in the form of optical energy from one or more pump sources36, examples of which are shown in FIGS. 4a-d. It will be appreciatedthat optical amplifiers 12 could include planar optical amplifyingdevices, and can be used in combination with semiconductor amplifiers.

The amplifying fiber 34 will generally be a doped and/or Raman fibersupplied with pump power in one or more pump wavelengths λ_(pi) suitablefor amplifying the signal wavelengths λ_(si) passing through theamplifying fiber 34. One or more dopants can be used in the dopedamplifying fiber 34, such as Er, other rare earth elements, as well asother dopants. The Raman fibers can include various silica-based fibers,e.g., pure, P-doped and/or Ge-doped silica fibers, such as thosecommonly used as transmission fiber, dispersion compensating fiber,etc., as well as other fiber material suitable for providing Raman gain.The doped and Raman fiber can be supplied in optical energy in variouspump wavelengths to amplify signal channels in other wavelengths. Forexample, signal channels in the 1550 nm wavelength range can beamplified by pumping an erbium doped fiber with pump power at variouswavelengths, such as 1480, and 980 nm. Likewise, Raman fibers can besupplied with pump power over a wavelength range, such as 1450-1480 nmto amplify signal channels in the 1550 nm wavelength range. Other signalwavelengths ranges can also be employed, for example 1300 nm, in theoptical system 10 as may be desired.

The amplifying fiber 34 can have the same or different transmission andamplification characteristics than the transmission fiber 14. Forexample, dispersion compensating fiber, dispersion shifted fibers,standard single mode fiber and other fiber types can be intermixed as orwith the transmission fiber 14 depending upon the system configuration.Thus, the amplifying fiber 34 can serve multiple purposes in the opticalsystem, such as performing dispersion compensation and different levelsof amplification, as well as lossless transmission and variableattenuation, of the signal wavelengths λ_(si).

The optical amplifier 12 can also include one or more serial and/orparallel amplifier stages, which may include combinations of one ormore, distributed and concentrated amplifier stages. The opticalamplifiers 12 may also include remotely pumped doped fiber or Ramanamplifying fibers 34 _(i) having different amplification andtransmission characteristics, e.g., dispersion, etc., than thetransmission fiber 14. The remotely pumped amplifying fiber 34 _(i) canbe pumped with excess pump power supplied to provide Raman gain in thetransmission fiber 14 or via a separate fiber. In addition, the opticalamplifier can include short lumped doped fiber amplifier stages operatedin deep saturation using pump power being supplied to other stages.

Other optical signal varying devices, such attenuators, filters,isolators, and equalizers can be deployed before, between, and aftervarious stages of the amplifier 12 to decrease the effective lossassociated with devices. Similarly, signal processing devices, such asadd/drop devices, routers, etc. can be included proximate the variousamplifier stages.

Pump energy can be supplied to the amplifying fiber 34 incounter-propagating and/or co-propagating directions with respect to thepropagation of the signal wavelengths λ_(si), as shown in FIGS. 4a-d. Itwill be appreciated that in a bi-directional system 10, the pumpwavelength λ_(pi) will be counter-propagating relative to signalwavelengths λ_(si) in one direction as well as co-propagating relativeto signal wavelengths λ_(si) in the other direction.

Pump power can be supplied separately to each amplifier stage or thepump power can be shared by splitting the pump power before it isintroduced into the amplifier or by streaming excess pump power from onestage to another. In addition, pump reflectors can be used to increasethe pump power utilization in one or more stages.

The pump source 36 can include one or more narrow and broad band lasers,or other coherent source, as well as incoherent sources, each providingpump power in wavelength bands centered about one or more pumpwavelengths λ_(pi). The pump wavelengths λ_(pi) can be combined usingcombiners 24, such as fused tapered and dichroic couplers, polarizationcombiners, etc., before being introduced into the transmission fiber 14.

In the present invention, the optical amplifier 12 further includes apump amplifier 40 configured to amplify the pump power being provided tothe amplifying media 34. The pump amplifier 40 can be variouslyconfigured similar to the optical amplifier 12 for the signal wavelengthλ_(si). The pump amplifier 40 will generally include pump amplifyingmedium 42 supplied with pump booster power in the form of optical energyin one or more pump booster wavelengths λ_(pbo) from a pump boostersource 44. It may also be possible to use semiconductor amplifiers asthe pump amplifier 40.

The pump amplifying medium 42 can be specifically tailored dependingupon the desired amount of gain from the pump amplifier 40. Varioustypes of amplifying medium can be used as discussed with respect to theamplifying medium 34 for the signal wavelengths λ_(si). Unlike in theamplifying medium 34, the selection of the pump amplifying medium 42 isnot limited by potential negative affects on the signal wavelengthcharacteristics, because the signal wavelengths λ_(si) do not passthrough pump amplifying medium 42.

The pump amplifier 40 can be used to provide Raman amplification of thepump power. For example, the pump booster source 44 can provide boosterpump power in the 850 nm and 1350 nm wavelength ranges to provide Ramanamplification of pump wavelengths in the 980 nm and 1450 nm wavelengthranges, respectively. The pump booster power can be co- and/orcounter-propagated relative to the pump wavelengths, althoughcounter-propagating the pump booster power relative to the pump powermay reduce interactions.

In various embodiments, the pump booster source 44 includes one or morehigh power semiconductor diodes, cascaded Raman resonators (“CRR”), aswell as other high power sources, configured to supply pump boosterpower to optically amplify the pump power being supplied to at least oneamplifying media. For example, commercially available CRRs from SDL,Inc. (San Jose, Calif.) have output wavelengths in the 1450-1480 nmrange. CRRs generally include a resonator configured to shift inputwavelengths λ_(pbi) of light through one or more Stokes shifts toprovide optical energy at successively longer wavelengths until aselected output wavelengths λ_(pbo) is reached. The number of Stokesshift performed by the CRR depends upon the particular configuration ofthe CRR.

Various CRRs are suitable for use in the present invention. For example,U.S. Pat. Nos. 5,323,404 and 5,623,508 describe CRRs that use spacedpairs of Bragg gratings to produce a resonator cavity. Each pair ofBragg gratings corresponds to one of the Stokes wavelengths between theinput wavelength and the desired output wavelength. Pairs of highreflectivity Bragg gratings are provided for each Stokes wavelengthintermediate to the input and the output wavelengths. Low reflectivityBragg gratings are provided at the inlet and outlet of the cavity toallow the input and output wavelengths into and out of the cavity,respectively.

Other CRR designs employ couplers and fiber rings to produce the Stokesshift. For example, in PCT International Publication No. WO 97/32378 anoptical wavelength converter is provided that employs one or more fiberrings optically linked via couplers to produce a corresponding number ofStokes shifts in the light wavelength. Another coupler embodimentincorporates a coupler connecting a fiber ring to a light source and ahigh reflectivity mirror is discussed by Chernikov et al., ElectronicsLetters, Apr. 2, 1998, v. 34, n. 7, Online No. 19980421.

The present invention also includes hybrid grating/combiner CRRembodiments that provide increased flexibility over conventional gratingand coupler CRR designs. The hybrid grating/combiner CRR embodimentsemploy input and output wavelength selective combiners, such as WDMcouplers, 46 _(i) and 46 _(o), generally corresponding to the input andoutput wavelengths, λ_(pbi) and λ_(pbo), respectively. Optical fiber 48or other Raman gain medium is used to interconnect two input wavelengthWDM coupler ports 50 _(i1) and 50 _(i2) with two output wavelength WDMcoupler ports 50 _(o1) and 50 _(o2) to produce a resonator cavity 52, asshown in FIGS. 6a&b. The input and output WDM couplers, 46 _(i) and 46_(o), can be designed to have a broad range of bandwidths in the inputand output wavelength range, respectively, to provide flexibility in theselection of the CRR source wavelengths.

In these embodiments, one or more input wavelengths λ_(pbi) are providedby an input wavelength source 47, such as one or more lasers, and areselectively introduced into the resonator cavity 52 through a thirdinput coupler port 50 _(i3). The input wavelength travels through theresonator cavity 52 and exits through a fourth input coupler port 50_(i4). A high reflectivity (˜100%) reflector 54 _(H) is position toreflect input wavelength light exiting the resonator cavity 52 throughthe fourth input coupler port 50 _(i4) back into the resonator cavity52.

Similarly, the output wavelength λ_(pbo) light selectively exits theresonator cavity 52 from third and fourth output wavelength WDM couplerports, 50 _(o3) and 50 _(o4). A low reflectivity (˜10%) reflector 54_(L) is positioned to reflect a portion of the output wavelength lightλ_(pbo) exiting through the third output coupler port 50 _(o3) back intothe resonator cavity 52 to provide feedback to the resonantor cavity 52.Another high reflectivity (˜100%) reflector 54 _(H) is position toreflect input wavelength light exiting through the fourth output couplerport 50 _(o4) back into the resonator cavity 52.

The resonator cavity 52 will generally be formed using optical fiber 54to interconnect the input and output WDM couplers. The optical fiber 54can include one or more optical fiber types that have different Ramangain and Stoke shifting characteristics relative to the input and outputwavelengths, λ_(pbi) and λ_(pbo), respectively. For example, small corefibers, such as dispersion compensating fibers, more efficiently promoteRaman gain and can be used to form the resonator cavity 52. The fiber 54will generally be formed in rings of various lengths for ease ofhandling, but can be formed in other shapes as may be appropriate.

The high reflectivity reflectors 54 _(H) can generally be highreflectivity, non-wavelength selective mirrors, although wavelengthselective reflectors, such as Bragg gratings, at the input and outputwavelengths can be used. The use of non-wavelength selective, highreflectivity reflectors provides additional flexibility in theconfiguring the CRR, because the reflectors do not constrain theselection of the input and output wavelengths of the CRR.

The lower reflectivity, wavelength selective reflector 54 _(L)(“feedback reflector”) provides feedback control over the outputwavelength λ_(pbo). The reflective bandwidth of the feedback reflector54 _(L) can be tailored to meet the required bandwidth of the outputwavelength for a system 10. Also, the feedback reflector 54 _(L) can betunable to provide additional flexibility in the output wavelength.Fixed or tunable fiber Bragg gratings, Fabry-Perot filters, and otherreflective devices, can be used as the high and lower reflectivityreflectors, 54 _(H) and 54 _(L). For example, FIG. 6b shows a morespecific embodiment, in which Bragg gratings are used as reflectors 54.

In various embodiments, pump booster power can be split and used toamplify pump power being provided to multiple amplifier stages disposedalong one or more transmission fibers 14. FIG. 7 shows an exemplaryembodiment, the pump booster power is divided using a distributor 26,such as a passive splitter, and supplied to the pump amplifying fibers42 in four separate pump amplifiers 40. In this manner, the pump boosterpower, which can be several watts and the cost associated with of thepump amplifier 40 can be spread over a number of optical amplifiers 12.It may be also be desirable to combine two or more pump booster sources44 using a combiner 24, such as a passive coupler, to provide additionalredundancy in the system, as further shown in FIG. 7.

Exemplary operation of the amplifier 12 of the present invention will bedescribed with regard to a Raman fiber amplifier in which the pump powerbeing supplied to the Raman fiber amplifier is amplified using Ramanpump amplifier. Signal wavelengths λ_(si) are transmitted from thetransmitters 18 to the receivers 20 through one or more of the opticalamplifiers 12 in this example.

The exemplary optical amplifier 12 is configured to receive pump powerranging from 1400-1500 nm range to amplify signal wavelengths λ_(si) inthe 1500-1600 nm range via Raman amplification. The pump source 36includes a plurality of laser diodes providing a plurality of pumpwavelengths λ_(pi) that can be counter- and/or co-propagated relative tothe signal wavelengths λ_(si) depending upon the system 10. The pumppower is passed through the pump amplifying fiber 42 and pump boosterpower in the 1300-1440 nm range from the pump booster source 44 iscounter-propagated through the pump amplifying fiber 42 to provide Ramanamplification of the pump power.

Those of ordinary skill in the art will further appreciate that numerousmodifications and variations that can be made to specific aspects of thepresent invention without departing from the scope of the presentinvention. It is intended that the foregoing specification and thefollowing claims cover such modifications and variations.

What is claimed is:
 1. An optical amplifier comprising: an optical fibermedium; a pump that supplies optical power in at least one pumpwavelength in the optical fiber medium; a pump amplifier that amplifiesthe pump optical power before the pump optical power is introduced intothe optical fiber medium, wherein the pump amplifier comprises: a pumpamplifying fiber connected between the pump and optical fiber medium; apump booster source connected to the pump amplifying fiber comprising anoptical power source and a cascaded Raman resonator, wherein thecascaded Raman resonator further comprises: an input wavelength combinerhaving first, second, and third input wavelength ports; an outputwavelength combiner having first, second, and third output wavelengthports; and, a Raman gain medium optically connecting the first andsecond input wavelength combiner ports with the first and second outputwavelength combiner ports to form a Raman resonator cavity, wherein thepump booster power exits the Raman resonator cavity at the outputwavelength through the third output wavelength port and optical power isintroduced through the third input wavelength port into the Ramanresonator cavity.
 2. The optical amplifier of claim 1, wherein theoptical power source is a semiconductor diode.
 3. The optical amplifierof claim 1, wherein the optical power source includes a plurality ofsemiconductor diodes.
 4. The optical amplifier of claim 3, wherein thehigh power semiconductor diodes all produce optical power at a commonwavelength.
 5. The optical amplifier of claim 3, wherein thesemiconductor diodes each produce optical power at a wavelengthdifferent then that produced by each other diode.
 6. The opticalamplifier of claim 3, wherein the input wavelength combiner includes a2×2 WDM coupler having first, second, third, and fourth input wavelengthports.
 7. The optical amplifier of claim 3, wherein the outputwavelength combiner includes a 2×2 WDM coupler having first, second,third, and fourth output wavelength ports.
 8. The optical amplifier ofclaim 6, wherein the fourth input wavelength port is optically connectedto a high reflectivity input reflector positioned to reflect inputwavelength optical power exiting the Raman cavity through the fourthinput wavelength port back into the Raman cavity.
 9. The opticalamplifier of claim 8, wherein the reflector includes a fiber Bragggrating.
 10. The optical amplifier of claim 7, wherein the fourth outputwavelength port is optically connected to a high reflectivity outputreflector positioned to reflect output wavelength optical power exitingthe Raman cavity through the fourth output wavelength port back into theRaman cavity.
 11. The optical amplifier of claim 10, wherein thereflector includes a fiber Bragg grating.
 12. The optical amplifier ofclaim 3, wherein the third output wavelength port is optically connectedto a low reflectivity output reflector positioned to reflect a portionof the pump booster power in the output wavelength exiting the Ramancavity through the fourth output wavelength port back into the Ramancavity.
 13. The optical amplifier of claim 12, wherein the reflectorincludes a fiber Bragg grating.
 14. The optical amplifier of claim 3,wherein the optical fiber medium is a Raman amplification medium. 15.The optical amplifier of claim 3, wherein the optical fiber medium isdoped with rare earth elements.
 16. The optical amplifier of claim 3,wherein the pump co-pumps the optical fiber medium.
 17. The opticalamplifier of claim 3, wherein the pump counter-pumps the optical fibermedium.
 18. The optical amplifier of claim 3, wherein the pump boostersource co-pumps the pump amplifying fiber.
 19. The optical amplifier ofclaim 3, wherein the pump booster source counter-pumps the pumpamplifying fiber.
 20. The optical amplfier of claim 3, wherein: theinput wavelength combiner includes at least a 2×2 WDM coupler havingfirst, second, third, and fourth input wavelength ports; the fourthinput wavelength port is optically connected to a high reflectivityinput reflector positioned to reflect input wavelength optical energyexiting the Raman cavity through the fourth input wavelength port backinto the Raman cavity; the output wavelength combiner includes at leasta 2×2 WDM coupler having first, second, third, and fourth outputwavelength ports; the fourth output wavelength port is opticallyconnected to a high reflectivity output reflector positioned to reflectoutput wavelength optical energy exiting the Raman cavity through thefourth output wavelength port back into the Raman cavity; and, the thirdoutput wavelength port is optically connected to a low reflectivityoutput reflector positioned to reflect a portion of the pump boosterpower in the output wavelength exiting the Raman cavity through thefourth output wavelength port back into the Raman cavity.